The present disclosure relates to receiving devices and methods, demodulating devices and methods, and programs, and particularly to receiving device and method, demodulating device and method, and program that enable enhancement in the accuracy of estimation of the SNR (Signal-to-Noise Ratio) relating to a propagation path.
As shown in FIG. 1, a digital terrestrial broadcast signal transmitted from a transmitting device 2 of a broadcast station or the like is received by a receiving device 1 via a propagation path 3. In the digital terrestrial broadcasting and so forth, e.g. OFDM (Orthogonal Frequency Division Multiplexing) is employed as the digital modulation system for data (signal).
The propagation path 3 gives the influence of noise and so forth to the signal transmitted from the transmitting device 2. In general, the influence given to the signal by the propagation path 3 is represented by the SNR.
In the receiving device 1, the path SNR of the propagation path 3, obtained from the signal transmitted from the transmitting device 2 via the propagation path 3, is estimated. Hereinafter, the estimated path SNR will be referred to as the estimated SNR.
FIG. 2 is a diagram showing the relationship between the ideal path SNR and the estimated SNR.
In FIG. 2, the estimated SNR represented by the axis along the vertical direction in the diagram is indicated by the dashed line, and the path SNR represented by the axis along the horizontal direction in the diagram is indicated by the solid line. As shown in FIG. 2, as the relationship between the estimated SNR (dashed line) and the path SNR (solid line), the value of the estimated SNR is closer to the value of the path SNR when the value of the SNR is larger. In contrast, the value of the estimated SNR is divergent from the value of the path SNR at a higher degree when the value of the SNR is lower.
The reason for the occurrence of such divergence will be described with reference to FIGS. 3A and 3B.
In the case of obtaining the estimated SNR from an unknown data signal included in a signal transmitted via the propagation path 3, generally the result of a hard decision for the constellation of the data signal is utilized. Specifically, when the path SNR is not low, the transmission point corresponds with the estimated transmission point in the constellation in the IQ plane as shown in pattern A of FIG. 3A, so that the ideal estimated SNR is obtained. In this case, the correct estimated SNR is obtained based on S and N indicated by the solid lines.
In contrast, as shown in pattern B of FIG. 3B, when the path SNR is low, the result of a hard decision is mistaken for an adjacent symbol and the transmission point does not correspond with the estimated transmission point. As a result, an erroneous estimated SNR is obtained. In this case, although the correct estimated SNR is obtained based on S and N indicated by the dashed lines, actually the erroneous estimated SNR is obtained by S′ and N′ indicated by the solid lines.
As a method for calculating the SNR, there has been disclosed an OFDM demodulating device that calculates the SNR based on a complex correlation signal obtained by complex correlation calculation of a baseband signal (refer to e.g. Japanese Patent Laid-open No. 2007-208748).